Sprockets are used, in machines of various kinds, to drive sprocket chains; and, in some of those machines, the sprockets are given heavy usage. When the teeth on a one-piece sprocket become worn to the point where that sprocket must be replaced, it usually is necessary to remove the shaft on which that sprocket is mounted, to replace that sprocket, and then to re-mount that shaft and its bearings. The cost of replacing a sprocket involves the time of one or more workmen, and usually involves the cost of replacing the anti-friction bearings for the shaft on which that sprocket is mounted. As a result, the cost of replacing a worn sprocket can be substantial.